Overhead maintenance apparatus



D 1965 J. s. HUBBARD OVERHEAD MAINTENANCE APPARATUS Filed Oct. 31, 1963 4 Sheets-Sheet 1 INVENTOR.

Dec. 21, 1965 J. 5. HUBBARD 3,224,528

OVERHEAD MAINTENANCE APPARATUS Filed 001:. 31, 1963 4 Sheets-Sheet 2 INVENTOR.

AZZ Jae U. WW //6 /ZO BY Dec. 21, 1965 J. s. HUBBARD 3,224,528

OVERHEAD MAINTENANCE APPARATUS Filed Oct. 31, 1963 4 Sheets-Sheet 5 Dec. 21, 1965 J. s. HUBBARD OVERHEAD MAINTENANCE APPARATUS 4 Sheets-Sheet 4 Filed Oct. 31, 1963 IN VENTOR.

United States Patent Ofiice 3,224,528 Patented Dec. 21, 1965 The present invention relates generally to apparatus for overhead maintenance work in industrial plants and elsewhere, and particularly to apparatus capable of raising one or more workmen to elevated positions at which the workmen may clean, repair or otherwise service such overhead equipment as light fixtures, electrical systems, springler systems, water, steam, air and oil lines, conveyor systems, ventilating and heating systems, and the like.

Two problems with existing overhead maintenance apparatus are that they are too bulky for use in the narrow aisles of many plants and that they lack sufiicient mobility to service many hard-to-reach and relatively inaccessible places. Thus, in many operations the presently known overhead service equipment cannot be employed; and instead, uneconomical and slower access equipment, such as scaffolding and ladders, must be used.

Accordingly, it is one object of this invention to provide overhead maintenance apparatus having a column or mast supporting a lift platform which is capable of carrying one or more workmen and which when positioned at the upper terminus of the supporting mast is movable outward from and above the mast.

It is a further object of this invention to provide overhead maintenance apparatus having a lift platform which is movable farther outward from the remainder of the unit than the platforms of the overhead maintenance equipment presently known.

It is another object of this invention to provide overhead maintenance apparatus having a lift platform which is movable throughout a greater area than the platforms of the overhead maintenance apparatus presently known.

It is also an object of this invention to provide overhead maintenance apparatus having a lift platform which is rotatable about an axis perpendicular to the horizontal plane of the base.

It is another object of this invention to provide overhead maintenance apparatus having a lift platform with sufiicient mobility to facilitate servicing of hard-to-reach and relatively inaccessible places.

A still further object of this invention is to provide overhead maintenance apparatus having a lift platform which is sufiiciently mobile so as to permit servicing of a maximum number of locations with minimum movement of the base.

Another object of this invention is to provide apparatus which greatly enhances the efiiciency and substantially reduces the cost of repairing, maintaining, and installing overhead equipment in industrial plants.

Another object of this invention is to provide apparatus which may be readily adapted for and greatly improves the efliciency of such outdoor maintenance operations as the servicing and repairing of street lighting fixtures.

Still another object of this invention is to provide apparatus which is easy and economical to operate and relatively inexpensive to maintain.

Additional objects will be manifest from a consideration of the drawings, description, and claims.

In accordance with one embodiment of this invention, overhead maintenance apparatus is provided having a base, preferably a mobile, self-propelled truck or the like, a turntable mounted on the base and rotatable relative to the base, and an extensible vertical mast or lift column mounted on the turntable and rotatable therewith.

A platform capable of carrying at least one workman is connected to the upper end of the mast, preferably by means of an arm which is pivotally connected both to the mast and to the platform. The platform is so arranged with regard to the remainder of the apparatus that it will remain in a substantially horizontal plane regardless of the angular position of the mast and arm. This arrangement permits the platform to be maneuvered around various equipment and piping and into small openings, many of which would be inaccessible when presently known methods and apparatus are employed.

For a more complete understanding of the present invention, drawings have been provided as follows:

FIGURE 1 is a perspective view of one embodiment of the present invention.

FIG. 2 is a back view of the embodiment of FIG. 1 showing only the mast and arm with the actuating mechanism of the arm exposed.

FIG. 3 is a perspective view of the actuating mechanism of the arm of the embodiment of FIG. 1.

FIG. 4 is a fragmentary perspective view of a modi-v fication of the platform and mast assembly shown in FIG. 1 and portions thereof cut away.

FIG. 5 is similar to FIG. 4 but showing another modification of the platform and'mast assembly of FIG. 1.

FIG. 6 is similar to FIG. 4 but showing a third modification of the platform and mast assembly of FIG. 1.

FIG. 7 is a fragmentary side view showing a modification of the embodiment of FIG. 1 and showing, in dotted lines, the arm thereof in various positions.

FIG. 8 is a fragmentary side view of the arm and platform of FIG. 7 illustrating the actuating mechanism of the arm in detail.

FIG. 9 is a bottom view of .the arm and platform assembly of FIG. 8, showing the two parallel sections of the arm in detail.

FIG. 10 is a fragmentary side view illustrating a modification of FIG. 7 in which the mast is mounted'on a turntable and the platform is shown in various positions relative to the base of the apparatus.

Referring now to FIGURE 1, one preferred embodiment 10 of the present invention is illustrated. The apparatus includes generally a suitable base 11, a turntable 12 mounted on the base and rotatable relative thereto, a telescoping mast 13 mounted on the turntable 12, and a battery box 14 containing a storage battery 19' and a counterweight 20 also mounted on the turntable. An arm 15 is pivotally connected at one end to a supporting member 21, extending at right angles from the mast 13 and forming a part thereof. The arm 15 is also pivotally connected at its other to a platform support 16 on which a platform 17 is mounted. The arm 15 may be adjusted to pivot in a vertical plane through an arc of approximately 180 degrees, and is also adapted to. move about a vertical axis together with the mast through an arc of 360 degrees. The base 11 is prefera-bly'any one of the self-contained, self-propelled, mobile types known to the art. It is preferably battery powered and supported by two drive wheels and two steering wheels 72. The turntable 12 may be of any suitable conventional design and is power operated and preferably torque controlled. Besides supporting the mast 13 and the battery compartment 14, the turntable may also support contactors and a fuse panel. The mast 13 is a conventional telescoping type, preferably having three or more sections. It may be actuated by a hydraulic cylinder through dual mechanical linkage having anti-friction guide bearings at load points. The hydraulic pump may .be a conventional electrically operated gear type controlled by an electrically operatedvalve and flow regulator. In the embodiment of FIG. 1 the mast section having the smallest diameter is on the bottom and the one with the greatest diameter is at the top (see FIG. 2).

Examples of a suitable turntable, turntable arrangement with respect to the base, and telescoping mast will be found in United States Letters Patent No. 3,095,945, issued July 2, 1963 to M. E. Mitchell. The mast 13 and battery box 14 are each mounted on the turntable 12 offset from the central axis thereof and are diametrically opposite each other. The turntable 12 is U-shaped, i.e., it is provided with two U-shaped flanges 18 which extend upward from the turntable 12 and support the battery compartment 14. Compartment 14 contains a battery 19 and a counterweight 20 which provides the necessary stability for the unit when the arm 15 and attached platform 17 are moved through their various positions of adjustment. The battery box 14 generally extends to a position outside the flanges 18 and the counterweight 20 is disposed in the portion of the box 14 which is outside the flanges 18. The battery 19, on the other hand, is generally positioned in that portion of the box between the flanges when used with a counterweight. The battery 19, in addition to supplying electrical power for operation of the unit 10, also acts as a counterbalance, and in some operations may be used alone as a counterweight. In such operations it is desirable to mount the battery in the outermost portion of battery box 14 so that the battery will be disposed at a greater distance from the center of the turntable 12 and from the mast 13. In this way the battery may act as a more effective counterbalance. In certain modified constructions of the present invention, the mast 13 may be disposed coaxially to the axis of rotation of the turntable 12.

The arm 15, best shown in FIGS. 2 and 3, is actuated by a hydraulic cylinder through dual mechanical linkage. The arm 15 comprises a frame 22, a hydraulic cylinder 24 welded orotherwise connected to the frame (FIG. 2 shows the cylinder 24 connected to the frame 22 by members 25 and 27), a piston 26 for movement within cylinder 24, and a trunnion 28 attached to the piston 26. The trunnion 28 is attached to two predetermined lengths of roller chain 30 which pass over four fixed sprockets 32. Two of the sprockets are secured to the mast portion 21 by bolts 34, and the other two are held to the platform support 16 by bolts 36. The frame 22 is attached at each end to bushings 38 which rotate about fixed shafts secured to the supporting member 21 and the platform support 16. A pump 40, actuated by an electric motor 42, forces hydraulic fluid from a supply tank 44 through a four-way solenoid valve 48 and into the hydraulic cylinder 24. Depending upon the position of the movable part of valve 48, fluid is either directed throughhydraulic hose 50 to the upper part of the cylinder 24 or through hydraulic hose 51 to the lower part of the cylinder, and the piston 26 is accordingly actuated inward or outward. When the piston is moved, it actuates the trunnion which in turn applies a force on the chain 30, causing the chain to wrap and unwrap about the sprockets 32 and thereby actuate the arm 15. Thus, if the piston is forced outward, it actuates the trunnion 28 away from the cylinder 24 and causes the trunnion to apply a force on the chain 30 which lowers the arm 15. If the piston is depressed, the trunnion 28 is moved toward the cylinder, applying an opposite force on thechain 30, which raises the arm 15. Travel of the arm 15 is regulated by the length of the cylinder stroke. Thus, a shorter cylinder stroke is used to reduce the distance in which the arm and attached platform travel in a vertical plane. This shorter stroke is accomplished by inserting stop tubes in the existing cylinders or by using a shorter stroke cylinder. The rate of speed of the arm 15 is controlled by flow resistors disposed in the hydraulic hoses 50 and 51 at the points where the hoses connect with cylinder 24. These resistors regulate the rate of flow of hydraulic fluid mcylinder 24 and provide a safety feature by preventing the arm 15 from falling in the event one or both of the hoses 50 and 51 break.

It is important that the chains 30 are sufficiently taut, and the length of the chains may be adjusted by altering the thickness of shims 52 (best shown in FIG. 2) which are positioned between plates 54 (see FIGS. 2 and 3) and trunnion 28. Chain length may also be adjusted by breaking the chain and employing a turnbuckle to secure the broken ends. Operation of the turnbuckle will then adjust the length of the chains.

Although valve 48 is preferably a four-way valve, a three-way valve or a two-way valve in combination with a check valve may be used in lieu thereof. If twoor three-way valves are used, only one hydraulic line would connect the valve 48 to the cylinder 24 and the fluid would be introduced at the bottom of the cylinder. The four-way valve is more desirable than the other valves because when using the latter valves, gravitational, rather than hydraulic, force is used to lower the arm 15 from a raised position. Hydraulic force is only utilized to raise the arm. Thus, when the arm 15 is adjusted to a position degrees from its retracted position, i.e., when the platform is at its uppermost position relative to the mast, the torque created by the weight of arm 15 may be insufficient to actuate it downward. Thus, to lower the arm from such a position the operator would have" to initiate the downward movement by pushing the arm 15 by hand or otherwise.

The pump 40 is a conventional gear-type, which is probably the most economical, but it may be a vanetype or piston-type pump. The motor 42 actuating the pump is a typical series wound 12, 24, or 36 volt electric motor. Electrical power is supplied to the motor 42 from the battery 19. Current from battery 19 is transmitted through coil cord 56 to terminal box 57, then to terminal box 58, and from there to the motor 42. The coil cord 56 is used because it extends and retracts in correspondence with the extension and retraction of the mast 13. When the mast is retracted, the excess cord 56 is contained in the cord receptacle 59. Any conventional hydraulic hose or flexible tubing 50 and 51 may be used to transport the hydraulic fluid to the various parts of the hydraulic system. The pump and motor referred to earlier for operating the mast are the same kinds as those used to operate the arm. In some applications only one pump and motor may be used to operate both the arm and the mast.

In the present invention, electrical energy for operating the hydraulic system may be supplied by a generator driven by an internal combustion engine, rather than by the battery 19; and, when the mobile base 11 is a highway truck, the hydraulic system may be driven by a power take-off from the truck engine, rather than by the battery 19. p

' The platform 17 is mounted on a platform support 16 which is secured to one end of arm 15. The platform generally comprises a floor 60, railing supports 62, and safety railings 64. The platform should be large enough to support at least one man. It should also be of such dimensions that it will contribute to the compactness of the overall unit.

The platform 17 may be fixed to the platform support 16, as shown in FIG. 1, or it may be connected in several other ways, as shown in FIGS. 4, 5, and 6.

FIG. 4 shows a modified platform unit 82 which could be substituted for the platform shown in the embodiment of FIG. 1. 'It will be noted that the modification 82 of FIG. 4 does not utilize an arm 15 like the one illustrated in FIG. 1 and described above. Such modification, however, could be combined with the arm 15. The modification 82 comprises a support 84 which is either welded or bolted at one end to the mast 13 and forms a part thereof and which extends outward from the mast 13 forming a right angle therewith. Mounted on the support 84 adjacent the distal end thereof is a turntable assembly 85, and mounted on the turntable assembly 85 is a platform 90. The platform should be sufficiently spaced from the mast 13 so that the platform may rotate without interference from the mast when the latter is fully retracted. The turntable assembly 85 comprises a turntable 86 secured to a toothed bearing 87 by bolts 88. The bearing 87 is attached to the support 84 and the turntable 86 is connected to the platform 90. The turntable 86 is actuated by an electrically powered motor 94, which drives a chain and sprocket assembly connected to bearing 87. The latter assembly comprises sprocket 95 and roller. chain 96 and is connected to motor 94 through a gear box 97, a V-belt 98, and V-pulleys 99 and 100.

FIG. 5 shows another modified platform unit 102. In this embodiment the unit 102 is provided with a support 104 welded, bolted, or otherwise joined at one end to the mast 13. The support 104, like support 84 of the embodiment of FIG. 4, extends outward from mast 13 at right angles thereto. Mounted on support 104 is a platform 106, which is adjustable outwardly and inwardly relative to the mast 13 along the fixed support 104. Since the platform 106 may be moved outward a substantial distance from mast 13, the servicing of normally hard-to-reach places is greatly facilitated when this platform unit is used. Movement of platform 106 is effected by an ordinary 12 or 24 volt series wound electric motor 108 which drives a rotatable shaft 110 connected to the motor by means of a V-belt 112, V-pulleys 113 and 114, and a gear box 116 in which the gear ratio is about 30:1. Attached to each end of the shaft 110 and rotatable therewith are sprockets 118 which engage roller chain 120. The chain 120 is secured at each end to the extreme ends of platform 106 so that when the sprockets 118 rotate, the platform 106 moves relative to the support 104. Cam followers or roller bearings 122 secured to each side of the support 104 by nuts 124 are provided for supporting the platform 106. The cam followers will rotate as the platform travels relative to support 104. A control panel 160, which will be hereinafter explained in greater detail, is mounted on the platform 106 for controlling movement of the platform, the mast, and the base.

FIG. 6 shows a further modification of the platform. In this embodiment a platform unit 130 is provided having a support member 132 and a platform 134. The support member 132 is rotatable about the vertical axis of the mast 13, which may be a telescoping type, through an arc of 360 degrees. Thus, the platform may be rotated to a position where it is in registration with the base so that no part of the platform will overhang the base. The platform may be manually driven although the illustrated embodiment shows the platform driven by an electric motor 136. Fixed to the underside of the support 132 is a sprocket 138. This sprocket engages roller chain 140, which in turn engages another sprocket 142; the latter sprocket being driven by electric motor 136 connected thereto through a V-belt 144, V-pulleys 146 and 148, and a gear box 150 in which the gear ratio is approximately 100:1. A support bearing collar, not shown, which is located immediately below sprocket 138 and is fixed to mast 13, retains the platform unit 130 at a fixed height relative to the top portion of the mast.

Referring again to FIG. I, mounted on one of the railing supports of the platform 17 nearest the mast is a control panel 160, which contains the electrical controls for positioning the various components of the unit 10. Thus, while standing on the platform 17, an operator may regulate movement of the arm 15, platform 17, mast 13, turntable 12, and base 11. The control panel may include a four position Joy Stick control 162 for regulating movement of the arm and platform 17, a 2-position lever type control for regulating upward and downward movement of the mast 13, and a push-pull emergency control for cutting off the electrical power regulating the upward movement on the arm and mast,

and all movement of the base and turntable. Also, the panel may contain a lever-type multi-position base travel and turntable control and a key-operated on-off switch.

Besides the controls located on the platform, there is a steering control 74 for regulating the direction of travel of the base. The steering control 74 operates the front wheels 72 through conventional mechanical steering linkage. Other controls may include automatic limit switches for preventing movement of the base when the mast or arm is in an extended position.

FIG. 7 illustrates a modification 200 of the apparatus 10 shown in FIG. 1. In unit 200 the mast 202, unlike the mast 13 of unit 10, is mounted directly on the base 204, rather than on a turntable, and is inclined rearwardly. Even though the mast 202 is not disposed on a vertical axis or on an axis perpendicular to the base 204 of the apparatus, it operates in substantially the same manner as the mast 13 shown in FIG. 1. The angle of inclination of mast 202 will vary from less than 1 to about 20 with respect to its vertical axis. By in-' clining the mast rearwardly, greater rearward reach is provided without the necessity of increasing the length of the offset arm 206 connected to the mast or the pivotal arm 208 attached to the offset arm. A further advantage is that, when the mast is fully retracted and the pivotal arm 208 is positioned in its forward extending direction (as shown in dotted lines in FIG. 7), the platform 209 secured to the outer end of the pivotal arm will be positioned in registration with a part of the base 204, so that portions of the platform will not project for wardly of the base.

The offset arm 206 is connected to the upper end of mast 202 and disposed in a plane substantially parallel to the plane of the base 204. The pivotal arm 208 is secured to the distal end of this offset arm 206. The pivotal arm 208 is similar to the arm 15 of the embodiment 10 of FIG. 1, except that it is split into two identical parallel sections 210 and 212 (see FIG. 9). Each section of arm 208 operates on the same principle as arm 15 and consists of the same component parts as that arm. Thus, section 210 comprises a frame 214, a hydraulic cylinder 216, a piston 218 for movement within the cylinder, a trunnion 220 connected to the exposed end of the piston, and roller chain 222 connected to the trunnion and passing over two sets of sprockets 224, 226, 228, and 230. Section 212 of arm 208 is constructed in the same manner as section 210.

Arm section 210 is attached to a bearing'232 (see FIG. 9) which is rotatably mounted on a shaft 234 (see FIG. 8), the latter being secured at one end to sprocket 228 and at the other end to sprocket 230. Sprocket 230 is secured to the outside surface of offset arm 206. Arm section 212 is similarly connected to a bearing 236 which is also mounted on a shaft, such shaft being secured at its opposed ends to sprockets 238 and 240. Sprocket 240, like sprocket 230, is secured to an outside surface of offset arm 206.

Since the sections 210 and 212 are attached to the outside surfaces of the offset arm 206, the pivotal arm may be adjusted to a forward substantially horizontal direction in which the upper portion of the-mast 202 and the offset arm 206 are disposed between the sections. The outer ends of the sections 210 and 212 are pivotally connected to brackets 241 and 242 depending from the central axis of the platform 209. Bracket 241 is secured to sprocket 226, and bracket 242 is secured to sprocket 245. Arm sections 210 and 212 are connected to bearings 246 and 247, respectively, and the bearings are rotatably mounted on shafts joined at each end to the sprockets. Thus, bearing 246 is mounted on shaft'248 (see FIG. 8), joining sprockets 224 and 226, and bearing 247 is mounted on a shaft joining sprockets 244 and 245. Here, again, the sections are connected relative to the outer surfaces of the platform so that the platform may 7 be adjusted to a forward position in which a portion of the platform is disposed between the arm sections.

The structure 200 illustrated in FIG. 7 does not include a turntable, and the inclined mast 202 is accordingly not rotatable relative to the base. Where an inclined mast is used, there is considerable overhang of the platform in certain positions of adjustment, and to maintain stability of the entire device it is necessary to position the battery and the counterweight a greater distance from the mast and generally adjacent the end of the base opposite the end closest to which the mast is disposed. In unit 200, battery 250 and counterbalance 252 are immediately adjacent the forward end of base 204. To mount the battery and counterbalance on a turntable in this embodiment would require a turntable of such diameter that the entire structure would be of an impractical width for normal operations. And, of course, to provide for the rotation of the mast on a turntable without having a counterbalancing weight disposed on the same turntable in diametric opposition to the mast would generally result in an unstable unit. Where the angle of mast inclination is less than degrees, however, it is possible to position the mast on a turntable even without such a counterbalancing weight thereon.

FIG. 10 shows an embodiment 260 in which an extensible mast 262 is slightly inclined and is mounted on a turntable 263. Diametrically opposed to the mast is a battery box 264 containing a battery 266 and a counterbalance 268. The operation and structure of the unit 260 of FIG. 10 are identical to unit 200 illustrated in FIG. 7, except that the unit 260 includes the turntable 263 on which the extensible mast 262 is mounted. The platform 270 of unit 260 is shown in FIG. 10 in various positions of rotation, illustrating the considerable flexibility of the unit. It will be seen that the telescoping mast 262 of unit 260 is provided with its widest section at the bottom, whereas the telescoping mast 13 of the embodiment 10 of FIG. 1 has its narrowest section at the bottom (see FIG. 2).

While several embodiments of this invention are shown above, it will be understood, of course, that the invention is not to be limited thereto, since many modifications may be made which fall within the true spirit and scope of this invention. It is contemplated, therefore, that any such modifications shall be covered by the appended claims.

Iclaim:

1. Overhead maintenance apparatus comprising: a 'mobile base; and extensible vertical telescoping mast mounted on said base; means for actuating said mast upward and downward; power means mounted on said base and disposed to one side of said mast for supplying energy to said apparatus; an offset arm having one end connected to the upper end of said mast; a second arm having one end pivotally connected to the other end of said offset arm; a platform pivotally connected to the other end of said second arm; means for actuating said second arm and platform in a vertical plane relatlve to the direction of movement of said base, said second arm and platform being movable to a position alongside said base.

3. The apparatus of claim 2 wherein a counterweight is mounted on said base adjacent said power means.

4. The apparatus of claim 3 wherein said power means is an electrical storage battery.

5. Overhead maintenance apparatus comprising: a mobile base; a turntable mounted there-on for rotation relative to said base; means for actuating said turntable; an extensible vertical telescoping mast mounted on said turntable; means for actuating said mast upward and downward; an offset arm having one end connected to the upper end of said mast; a second arm having one end pivotallyconnected to the other end of said offset arm; a platform pivotally connected to the other end of said second arm; means for actuating said second arm and platform in a plane transverse to the direction of movement of said base, said second arm and platform being movable to a position alongside the mast where the platform is in a retracted position adjacent to and overlying a portion of said base; means for maintaining said platform in a horizontal position in all degrees of movement of said second arm and means mounted on said turntable for supplying power to said apparatus and for counterbalancing the Weight of the second arm and platform in all degrees of movement of said arm and platform.

6. The apparatus of claim 5 wherein said mast is inclined at angles of up to about 10 relative to an axis taken perpendicular to the direction of movement of said base.

7. The apparatus of claim 6 wherein said mast is eccentrically mounted on said turntable and is inclined away from the central axis of said turntable and said power and counterbalancing means is eccentrically mounted on said turntable opposite to said mast.

8. The apparatus of claim 7 wherein said power and counterbalancing means comprises an electrical storage battery and counterweight.

9. Overhead maintenance apparatus comprising: a mobile base; a turntable mounted thereon for rotation relative to said base; means for actuating said turntable; a mast eccentrically mounted on said turntable, said mast having a plurality of telescoping sections; means for actuating the mast sections upward and downward; a counterbalancing compartment mounted on said turntable diametrically opposite said mast, said compartment having mounted therein means for supplying electrical energy to said apparatus and a counterweight; an offset arm connected to the upper section of said mast; a pivotal arm having one end pivotally connected to said offset arm; a platform pivotally connected to the other end of said pivotal arm; means for actuating said pivotal arm and platform in a vertical plane relative to said base, said pivotal arm and platform being movable to a position alongside the mast where the platform is in a retracted position adjacent to and overlying a portion of said base; means for maintaining said platform in a horizontal position in all degrees of movement of said pivotal arm.

10. Overhead maintenance apparatus comprising: a mobile base; an extensible mast mounted thereon adjacent the rear end of said base, said mast being rearwardly inclined; means for actuating said mast; a counterbalancing compartment mounted on said base adjacent the front end thereof, said counterbalancing compartment having mounted therein means for supplying electrical energy to said apparatus and a counterweight; an olfset arm connected to the upper end of said mast; a pivotal arm having two parallel sections, each section having one end pivotally connected to the outer surfaces of said offset arm so that said offset arm and said mast are disposed between said sections; a platform pivotally connected to the other ends of said sections of the pivotal arm in- .termediate the ends of said platform, said platform being positioned between said sections of said pivotal arm,

said pivotal arm and said platform being adjusted to 'swing in a vertical plane relative to said base through an arc of greater than and less than 270, said platform having a retracted position in substantial registration with the front end of said base; means for actuating said arm and platform; means for maintaining said platform in a horizontal position in all degrees of rotation of said pivotal arm.

11. The apparatus of claim 10 wherein said apparatus includes a turntable mounted on said base and means for actuating said turntable, and said mast is eccentrically mounted on said turntable and is slightly inclined, and said counterbalancing compartment is eccentrically mounted on said turntable opposite said mast.

References Cited by the Examiner UNITED STATES PATENTS Girardi 1822 X Balogh 182-63 Hill 182-63 Hotchkiss 1822 Mitchell 182-63 Volkel 1822 Mitchell 182-63 X Pierce 1822 X HARRISON R. MOSELEY, Primary Examiner. REINALDO P. MACHADO, Examiner. 

1. OVERHEAD MAINTENANCE APPARATUS COMPRISING: A MOBILE BASE; AND EXTENSIBLE VERTICAL TELESCOPING MAST MOUNTED ON SAID BASE; MEANS FOR ACTUATING SAID MAST UPWARD AND DOWNWARD; POWER MEANS MOUNTED ON SAID BASE AND DISPOSED TO ONE SIDE OF SAID MAST FOR SUPPLYING ENERGY TO SAID APPARATUS; AN OFFSET ARM HAVING ONE END CONNECTED TO THE UPPER END OF SAID MAST; A SECOND ARM HAVING ONE END PIVOTALLY CONNECTED TO THE OTHER END OF SAID OFFSET ARM; A PLATFORM PIVOTALLY CONNECTED TO THE OTHER OF THE SAID SECOND ARM; MEANS FOR ACTUATING SAID SECOND ARM AND PLATFORM IN A VERTICAL PLANE RELATIVE THE DIRECTION OF MOVEMENT OF SAID BASE, SAID SECOND ARM AND PLATFORM BEING MOVABLE TO A POSITION ALONGSIDE THE MAST WHER THE PLATFORM IS IN A RETRACTED POSITION ADJACENT TO AND OVERLYING A PORTION OF SAID BASE; MEANS FOR MAINTAINING SAID PLATFORM IN A HORIZONTAL POSITION PARALLEL TO THE HORIZONTAL PLANE OF THE BASE IN ALL DEGREES OF ROTATION OF SAID PLATFORM. 